After about 20 minutes of driving and then under acceleration (doesn't matter what gear) she'll lose power and start to back fire if I keep the accelerator held down. I can let up and she'll do fine until I get into it again. A mechanically skilled friend suggested that my C-converter may be clogging up. I had it on a 5 hr trip and she started acting up again so I pulled over and beat the converter with a hammer. Got in and it worked fine, for about 20 minutes. After 5 hrs of that I pretty much had it in my head that the converter was the problem so I had it replaced. That wasn't it So on my way back to TN I got the idea to just kill the ignition while still coasting at 55 mph. I started it back up and she did fine for about 20 minutes. I checked fuel pressure, about 40psi with the key on and 38 with the engine running. I changed the filter and the upstream side came out looking like a chocolate milkshake. I thought for sure thats it.
It wasn't I have done wires and plugs. The plugs had a good color but the exhaust guy said he thought it was running way rich. My mpg is about 22 with a five speed and a 3.08 rearend. Any ideas?

Spark or timing I haven't gotten to yet, but yes I was thinking about that also. I'm also wondering if maybe the fuel pump has good pressure at idle but not able to keep up with volume under high demand.

I have about the same problem with mine. It started out as a rough idle at first start. Checked the codes and it said the iac and o2 sensor bank 1. Changed them out and the problem for me has been getting really bad. It will do fine sometimes. But most of the time it will just fall on its face. I took it to a shop and they said after testing, they think the computer is going into limp home mode. When I asked what would cause it, He said he had no clue. Has anyone else had this problem and been able to solve it? When it acts up, its like all of the fuel or spark is cut off only letting it idle.

I have about the same problem with mine. It started out as a rough idle at first start. Checked the codes and it said the iac and o2 sensor bank 1. Changed them out and the problem for me has been getting really bad. It will do fine sometimes. But most of the time it will just fall on its face. I took it to a shop and they said after testing, they think the computer is going into limp home mode. When I asked what would cause it, He said he had no clue. Has anyone else had this problem and been able to solve it? When it acts up, its like all of the fuel or spark is cut off only letting it idle.

Ok. Codes are 0171, 0136, 1131, 1151, and 0174. Of course all of them starting with a P. I have the iac unhooked right now because it revs up to 2500rmp while it is rolling. But back to normal when you stop.